The invention concerns a method for connecting two or more superconducting wires, each comprising at least one filament that contains MgB2, wherein the superconducting connection is realized by exposed end regions of the filaments via a superconducting matrix.
A method of this type is disclosed in U.S. Pat. No. 7,226,894 B2.
Superconducting wires, through which an electric current can flow without loss, are used in a plurality of ways, in particular, for high-field magnet coils. Superconducting materials thereby become superconducting only below a material-specific transition temperature TC such that superconducting materials must be cooled for technical use. One of the most important superconducting materials in the technical field is NbTi which has a transition temperature of approximately 10K. Since this low transition temperature requires cooling with cryogenic helium (boiling point approximately 4K), the use of NbTi is relatively expensive.
In 2001, superconductivity was discovered in the Mg—B system, which enables relatively inexpensive cooling without cryogenic helium with a transition temperature of approximately 39K for MgB2. For this reason, the operating costs of technical systems could be reduced and the ease of maintenance be increased. MgB2 also has a higher critical magnetic field Bc2 compared to NbTi. For this reason, the superconducting system MgB2 is currently the subject matter of numerous research and development activities.
One difficulty with the technical use of the MgB2 superconducting system is the provision of superconducting connecting points (“joints”), in particular, between two MgB2 superconducting wires. The quality of the superconducting connecting points thereby delimits the efficiency of the overall superconducting system.
U.S. Pat. No. 6,921,865 B2 discloses a joint of two superconducting wires, wherein exposed NbTi filaments of the superconducting wires project into bulk MgB2 powder and are compressed therewith.
DE 39 05 424 C2 describes a method for connecting oxidic superconductors, in which their contact surfaces are thermally melted.
U.S. Pat. No. 7,226,894 B2 discloses a connection between two MgB2 superconducting wires, wherein the MgB2 filaments are exposed at the ends of two superconducting wires and are overlapped. The exposed ends are then heated together with a mixture of boron powder and magnesium powder, wherein boron and magnesium react to form MgB2. The generated MgB2 superconductingly connects the two wires. The generated MgB2 is, however, highly porous and the resulting current carrying capacity of the joint is relatively small.
DE 10 2006 020 829 A1 describes a superconductive joint with superconducting wire conductor leads made from e.g. MgB2. Free conductor lead ends are thereby disposed in a bushing containing bulk MgB2 powder. The bulk powder is subsequently compressed together with the bushing.
EP 0 280 812 B1 discloses various compositions of high temperature superconductors, in particular, of the YBCO-type.
It is the underlying purpose of the invention to improve the quality, in particular, the current carrying capacity and critical magnetic field strength of a superconducting connection of MgB2 superconducting wires.